The Morokweng impact structure is an impact structure buried beneath the Kalahari Desert near the town of Morokweng in South Africa's North West province, close to the border with Botswana.[1]
| Morokweng impact structure | |
|---|---|
  Location of the impact structure in South Africa | |
| Impact crater/structure | |
| Confidence | Confirmed |
| Age | 146.06 ± 0.16 Ma |
| Exposed | No |
| Drilled | Yes |
| Bolide type | LL chondrite |
| Location | |
| Coordinates | 26°28′00″S 23°32′00″E / 26.466667°S 23.533333°E |
| Country | South Africa |
| Province | North West |
Description
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Estimates of the diameter of the structure vary widely with some studies suggesting a smaller size of 75–80 km (47–50 mi) in diameter while others suggests a much larger size of around 240 km (150 mi) or more. Its age is estimated to be 146.06 ± 0.16 million years, placing it within the Tithonian stage of the Late Jurassic, several million years before the Jurassic–Cretaceous boundary.[2][3][4] Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and gravimetric surveys. Core samples have shown it to have been formed by the impact of an L chondrite asteroid estimated to have been 5 to 10 km (3.1 to 6.2 mi) in diameter.[5]
In May, 2006, a group of scientists drilling into the site announced the discovery of a 25 cm (9.8 in)-diameter fragment of the original asteroid at a depth of 770 m (2,530 ft) below the surface, along with several much smaller pieces a few millimetres across at other depths. This discovery was unexpected, since previous drillings on large impact structures had not produced such fragments, and it was thought that the asteroid had been almost entirely vaporised.[6] Some of the fragments can be seen in the Antenna Wing of London's Science Museum.
References
edit- ^ "Morokweng". Earth Impact Database. Planetary and Space Science Centre University of New Brunswick Fredericton. Retrieved 9 October 2017.
- ^ Kenny, G.G., Harrigan, C.O., Schmitz, M.D., Crowley, J.L., Wall, C.J., Andreoli, M.A., Gibson, R.L. and Maier, W.D., 2021. Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa. Earth and Planetary Science Letters, 567, no. 117013, 13 p.
- ^ Schmieder, M. and Kring, D.A., 2020. Earth's impact events through geologic time: a list of recommended ages for terrestrial impact structures and deposits. Astrobiology, 20(1), pp.91-141.
- ^ Andreoli, M. A. G., et al. "The 144 Ma Morokweng impact crater, South Africa: geophysical and borehole evidence for a~ 240 km structure." 10th SAGA Bienniak Technical Meeting and Exhibition. 2007.
- ^ Mcdonald, I., Andreoli, M.A.G., Hart, R.J. and Tredoux, M., 2001. Platinum-group elements in the Morokweng impact structure, South Africa: Evidence for the impact of a large ordinary chondrite projectile at the Jurassic-Cretaceous boundary. Geochimica et Cosmochimica Acta, 65(2), pp.299-309.
- ^ Maier, WD; Andreoli MA; McDonald I; Higgins MD; Boyce AJ; Shukolyukov A; Lugmair GW; Ashwal LD; Graser P; Ripley EM; Hart RJ (11 May 2006). "Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa". Nature. 441 (7090): 203–6. Bibcode:2006Natur.441..203M. doi:10.1038/nature04751. PMID 16688173. S2CID 4373614.
Further reading
edit- Morelle, Rebecca (10 May 2006). "Relic of ancient asteroid found". BBC News. Retrieved 31 May 2006.
- Peplow, Mark (10 May 2006). "Meteorite survivor unearthed". Nature. doi:10.1038/news060508-7. S2CID 129248764.
External links
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